Fossil fuels such as coal contains sulfur compounds as impurities, and most of sulfur content is exhausted as sulfur dioxide upon combustion under excess of oxygen. Sulfur dioxide contained in exhaust gas is generally removed by wet process using a scrubber to contact exhaust gas with the mist of absorbent and absorb and remove sulfur dioxide (Refer, for example, to the Japanese laid open Patent Application (JP H10-202049-A)).
A dry exhaust gas treating method is also known which oxidizes sulfur dioxide gas by passing sulfur dioxide in exhaust gas through pulsed corona discharge region, and removes it by adsorbing on fine powder of calcium oxide or others as an adsorbent (Refer, for example, to the Japanese laid open Patent Application (JP H05-228330-A)). Further, the art to convert sulfur dioxide gas to sulfur trioxide gas with vanadium pentoxide (V2O5) as an oxidizing catalyst was disclosed in the Japanese laid open Patent Application (JP 2001-11041-A).
However, by the exhaust gas treating method of wet process, big plant investment is required, and an apparatus itself is large-sized due to required large amount of water, and therefore, it is not easily utilized where water resource is scant. Also by the exhaust gas treating method of dry process, high cost is required due to the use of additives and oxidative catalysts.